Manufacture of chromates



Patented Feb. 17, 1925.

UNITED STATES PATENT OFFICE.

LOUIS CHARLES DBEFAHL, 01? LAKEWOOD, OHIO, ASSIGNOR TO THE GRASSELLI CHEM.-

' IGAL OOMIPANY, OF CLEVELAND, OHIO, A CORPORATION OF OHIO.

MANUIFAGTUBE GHBOIATES.

in; Drawing.

accepted practice for the production of chromium salts, chromium oxid or finely divided chromium ore or chromium bear ng material is mixed wlth a compound'of an alkali-forming metal such as, alkali or al-' -kaline earth metal oxid, hydroxid or car- 9 bonate or mixtures thereof, and the mixture is roasted at a suitable temperature in either a reverberatory of mufile furnace in the presence of a .l argc excess of air. During the roasting o eration the mixture is stirred or rabbled eit. er mechanically or by hand. In such processes the heat necessary to raise the constituents of the mixture to. reaction temperature isderived from the burning of A 3 fuel extraneously of the mixture in a suitable fire box' or combustion chamber.

According to one common method of making chromate salts from chromium ore a char e consisting of ore, soda ash and lime in suitable pro ortions is roasted in a hand 36 operated rever atory furnace externally fired with coal, the charge being introduced into the furnace at a point remote from the bridge wall and advanced b hand through the furnace toward the bri go Well 40 as the oxidation pro About six or eight -.hours are required for the complete roasting of a batch of ore. The temperature proceed favor-; ably is in the neighborhood of 15009 F. The

at which oxidation seems to f roasted mass is then leached for the recove of soluble chromium salts. v

n this process and thc'other known procomes referred to the presence of unconof known .apparatus. the charge generates sufliclent heat to bring Application filed March 1, 1923. Serial No. 622,206.

tice the presence of lime in the furnace batch is necessary in order to avoid fusing of the mass wherebyoxidation would be impeded. The presence of lime in the batch however results in a considerable loss of chromium due to the formation of calcium chromate and other calcium containing chromium compounds which are not readily dissolved in the dissolution process.

While carrying on development work on the oxidation of chromium ores by means processes for the purpose of ascertaining the conditions necessary for maximum recovery of chromium salts it oc-' curred to me that the oxidation might be successfully carried out in a very unusual manner which, for convenience, I shall call blast-roasting. According to this process instead of heating the chromiummontaining material by the combustion of-fuel extraneously of the charge, the fuel is mixed with the chromium-containing material and the mixture is treated in a suitable apparatus suchas :1. Hunton-Heberlein sintering pot or a Dwight-L oyd continuous sintering The combustion ofqthe fuel in the entire mass to a temperature suitable for the proper absorption of oxygen in the form of atmospheric air or oxygen applied to the mass either by suction or blast. 7 In applying the new rocess to the manufacture of chromates, prefer to operate with mixtures of chromium ore or chromium bearing material, soda ash and a suitable fuel, preferably petroleum coke or charcoal. The proportions of the constituents will vary to a considerable degree dependmg upon the nature and composition of the chromium bearing material and the fuelfemployed. Any suitable fuel may be employed such as petroleum coke, charcoal, coke, coal, tars and oils.

Petroleum coke and charcoal are' preferred because they contain very small amounts of ash producing constituents.

According to my process lime is not a necessary constituent of the charge but a suflicient water to form a mass suitable for feeding. r

The-charge is'fed into suitable sintering apparatus in which the fuel of the charge .is burned by a strong blast of air supplied either by suction or by blast whereby the charge is brought to a suitable temperature for the oxidation of the chromium content of the charge to a higher state of oxidation with the concomitant formation of chromate salts. It is of course understood that air or oxygen is supplied in quantity sufficient to burn the fuel and also supply oxygen for the oxidation of the chromium content of the charge.

The roasted or sintered charge is then leached in the usual manner for the recovery of chromate salts.

In the above example the charge contains lime but this may beomitted. v

The proportions of the charge will vary widely, depending not only upon the nature of the constituents of the charge but also upon the size of the charge. In general the amount of fuel required for a charge is determined by the amount necessary to bring the reactingmass to a temperature at which rapid oxidation will take place, such temperature being in the neighborhood of 1500 F. or higher. In applying the new process for the oxidation of chromium ores or compounds it has been found to be pos- SlblB" to reduce the time required for oxidation to a fraction of that required in the hand furnacing operation described above. The process can be carried out in simple apparatus oecu iying little space and give an excellent yie d and comparatively large production. The initial cost of apparatus is materially reduced and there is a material Ewing in maintenance, operating labor, and

This application is a continuation in part of my application Serial No. 532,874, filed January 30, 1922.

I claim:

1. Process of oxidizing chromium compounds which comprises blast roasting a mixture of the same with a carbonaceous fuel and a compound of an alkali forming metal at a temperature in the neighborhood of 1500 F.

2. Process of oxidizing chromium compounds which comprises mixing the same with a compound of an alkali forming metal and carbonaceous fuel in quantity suflicient when burned to heat the mixture to a temperature at which the chromium compounds react with oxygen, and burning said fuel in the presence of an excess of oxygen.

3. Process of oxidizing chromium compounds which comprises mixing the same with a compound of an alkali forming metal and a carbonaceous fuel substantially free from ash forming constituents, and burning said fuel in the presence of an excess of oxygen. 'j H 4. Process of making ehromates wh1ch comprises blast-roasting a mixture of a chromium compound with a carbonaceous fuel and a compound of an alkali-forming metal.

5. Process of making ehromates which comprises forming a mixture of chromium ore, carbonaceous fuel and a compound of 'an alkali-forming metal, said fuel in quantity sufficient when burned to heat the mixture to at least 1500 F, and burning the fuel in said mixture in the of oxygen.

6. Process of making ehromates which comprises forming a mixture containing presence ofan excess chromium oxid, a compound of an alkalimetal, a compound of an alkaline earth 'metal, and a carbonaceous fuel in quantity suflicient when burned to heat the mixture to at least 1500 F., and burning said fuel in the presence of an excess of oxygen.

7. Process of making ehromates which comprises forming a mixture comprising a chromium ore, an alkali metal carbonate,

. and a carbonaceous fuel in quantity suflicientwhen burned to heat the mixture to a temperature at which oxidation of the chrm miuan content of the ore will take place, and burning said fuel in a blast of air.

8. Process of making ehromates which comprises forming a mixture comprising 100 parts of chromium ore, 80 parts of soda ash and 67 parts of carbonaceous fucl, and blastroasting said mixture. a

9. Process of making chromates which comprises forming a mixture comprising 100 parts of chromium ore, 110 parts of lime, 80 parts of soda aslnand 67 parts of carbonaceous fuel, and blast-roasting said mixture.

10. Process of making ehromates which comprises forming a mixture comprising a chromium oxid ore, an alkali metal carbonate and petroleum coke and heating said mixture to at least 1500 F. in the presence 5 of free oxygen. 4

11. Process of making chromates. which compyises heating a mixture of a chromium compound, a compound of an alkali-forming metal and a carbonaceous fuel to oxidizing temperature solely by combustion of the 10 fuel.

In testimony whereof, I aflix my signature.

LOUIS CHARLES DREFAHL. 

